Optical inspection system, illumination apparatus and method for use in imaging specular objects based on illumination gradients

Abstract

An optical inspection system uses an illumination gradient to gradually spatially vary the intensity and/or specular characteristics of the illumination reflected from the surface of a specular object to determine surface gradients of the object. The surface gradients can be used to reconstruct a three-dimensional image of the object. The illumination gradient can be produced by an illumination apparatus that includes circular arrays of light-emitting elements. The illumination gradient can also be produced using an optical element that gradually alters the illumination intensity of the reflected illumination in accordance with the incidence characteristics of the reflected illumination on the optical element. The illumination gradient enables the use of numerous illumination angles to reduce error in estimated surface gradients without increasing imaging or processing time.

We claim:  
     
         1 . An optical inspection system, comprising: 
 means for receiving illumination reflected from the surface of an object; and    means for producing image data representing the intensity of the reflected illumination from spatial locations on the surface of the object; and    means for processing said image data to discern between illumination intensities of an illumination gradient associated with the reflected illumination to determine surface gradients at the spatial locations on the surface of the object.    
     
     
         2 . The optical inspection system of  claim 1 , further comprising: 
 light-emitting elements disposed in concentric circular arrays around an axis orthogonal to a plane in which the object is located, said light-emitting elements producing the illumination gradient across at least a contiguous portion of said light-emitting elements.    
     
     
         3 . The optical inspection system of  claim 1 , further comprising: 
 an optical element disposed between the object and said means for receiving to produce the illumination gradient by altering the illumination intensity of the reflected illumination over angles of incidence of the reflected illumination on said optical element.    
     
     
         4 . The optical inspection system of  claim 1 , wherein said means for receiving comprises a sensing apparatus disposed relative to the object to receive the reflected illumination and said means for producing comprises an optical image sensor within said sensing apparatus.  
     
     
         5 . An illumination apparatus for use in an optical inspection system, comprising: 
 light-emitting elements disposed in concentric circular arrays around an axis extending from a plane in which an object under inspection is located, said light-emitting elements being configured to illuminate the object with illumination characterized by at least one illumination parameter having an illumination gradient across at least a contiguous portion of said light-emitting elements.    
     
     
         6 . The illumination apparatus of  claim 5 , further comprising: 
 a support structure including an inside surface on which said light-emitting elements are mounted to position said light-emitting elements at different azimuths and elevations with respect to the object.    
     
     
         7 . The illumination apparatus of  claim 5 , wherein the light-emitting elements are configured to produce the illumination gradient in elevation.  
     
     
         8 . The illumination apparatus of  claim 5 , wherein the light-emitting elements are configured to produce the illumination gradient in azimuth.  
     
     
         9 . The illumination apparatus of  claim 8 , wherein the light-emitting elements are configured to produce the illumination gradient in at least two different azimuths.  
     
     
         10 . The illumination apparatus of  claim 5 , wherein the at least one illumination parameter comprises illumination intensity.  
     
     
         11 . The illumination apparatus of  claim 10 , wherein the at least one illumination parameter comprises at least one spectral characteristic of the illumination.  
     
     
         12 . An optical inspection system for inspecting an object, comprising: 
 a sensing apparatus disposed in relation to the object to receive illumination reflected from the surface of the object, said sensing apparatus being configured to produce image data representing the intensity of the reflected illumination from spatial locations on the surface of the object, the image data for use in determining surface gradients at the spatial locations on the surface of the object; and    an optical element disposed between the object and said sensing apparatus to produce an illumination gradient by altering the illumination intensity of the reflected illumination over incidence characteristics of the reflected illumination on said optical element.    
     
     
         13 . The optical inspection system of  claim 12 , wherein said optical element is selected from the group consisting of: a patterned aperture window of said sensing apparatus, a directionally-selective aperture window of said sensing apparatus, a patterned filter disposed in front of an aperture of said sensing apparatus, a directionally-selective filter disposed in front of the aperture of said sensing apparatus, a patterned lens of said sensing apparatus, a directionally-selective lens of said sensing apparatus and a transmissive liquid crystal display screen disposed in front of the aperture of said sensing apparatus.  
     
     
         14 . The optical inspection system of  claim 12 , further comprising: 
 four or more collimated light sources disposed in relation to the object to selectively illuminate the object with different angles of incidence.    
     
     
         15 . An optical inspection system for inspecting an object, comprising: 
 an illumination source disposed in relation to the object to illuminate the object with illumination characterized by at least one illumination parameter having an illumination gradient; and    a sensing apparatus disposed in relation to the object to receive illumination reflected from the surface of the object, said sensing apparatus being configured to produce image data representing the illumination parameter of the reflected illumination from spatial locations on the surface of the object, the image data for use in determining surface gradients at the spatial locations on the surface of the object to reconstruct a greater than two-dimensional image of the shape of the surface of the object.    
     
     
         16 . The optical inspection system of  claim 15 , wherein said illumination source comprises a light ring including light-emitting elements disposed in concentric circular arrays around an axis of an aperture of said sensing apparatus, the axis extending from a plane in which the object is located, said light-emitting elements being configured to produce the illumination gradient across at least a contiguous portion of said light-emitting elements.  
     
     
         17 . The optical inspection system of  claim 16 , further comprising: 
 an illumination control circuit connected to control the illumination intensities of each of the light-emitting elements to produce the illumination gradient.    
     
     
         18 . The optical inspection system of  claim 16 , further comprising: 
 a support structure including an inside surface on which said light-emitting elements are mounted to position said light-emitting elements at different azimuths and elevations with respect to the object.    
     
     
         19 . The optical inspection system of  claim 16 , wherein the light-emitting elements are operable to produce the illumination gradient in elevation in a first illumination configuration.  
     
     
         20 . The optical inspection system of  claim 19 , wherein the light-emitting elements are further operable to produce the illumination gradient in azimuth in a second illumination configuration, said sensing apparatus being operable to capture a separate image of the surface of the object under the first and second illumination configurations, said first illumination configuration producing the image data to determine the surface gradients of the object and the second illumination configuration producing the image data to determine the orientation of the surface gradients of the object.  
     
     
         21 . The optical inspection system of  claim 20 , wherein the second illumination configuration comprises at least two different azimuthal illumination configurations, said sensing apparatus being operable to capture a separate image of the surface of the object under the first illumination configuration and the two different azimuthal illumination configurations, said first illumination configuration producing the image data to determine the surface gradients of the object and the two different azimuthal illumination configurations collectively producing the image data to determine the orientation of the surface gradients of the object.  
     
     
         22 . The optical inspection system of  claim 15 , wherein the at least one illumination parameter comprises illumination intensity.  
     
     
         23 . The optical inspection system of  claim 22 , wherein the at least one illumination parameter comprises at least one spectral characteristic of the illumination.  
     
     
         24 . A method for inspecting an object using an optical inspection system, comprising: 
 receiving illumination reflected from the surface of an object;    producing image data representing the intensity of the reflected illumination from spatial locations on the surface of the object; and    in response to said image data, discerning between illumination intensities of an illumination gradient associated with the reflected illumination to determine surface gradients at the spatial locations on the surface of the object.